• Journal of the Korean Magnetics Society
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• v.8 no.1
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• pp.1-5
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• 1998

Acicular Fe-Co alloy particles are one of the candidates for high-density magnetic recording media. We examined the effects of Co additions on the magnetic properties of Fe-Co alloy particles by using M$\'{o}$ssbauer spectroscopy, TEM, and X-ray diffraction. Acicular $Fe_n$Co (n=5, 4, 3, 2) alloy particles coated with silica, were prepared by a chemical coprecipitation method and subsequent H $_2$ reduction. The crystal structure was found to be cubic in all n ranges. The lattice constant $a_0$ decreases with increasing Co contents. Analysis of $^{57}Fe$ M\'{o}$ssbauer effect data in terms of the local configurations of Co atoms has permitted the influence of magnetic hyperfine interactions to be monitored.

• Journal of the Korean Ceramic Society
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• v.46 no.6
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• pp.621-626
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• 2009

Fe-AC/Ti$O_2$ photocatalysts were prepared by a sol-gel method. The photocatalytic properties of Fe-AC/Ti$O_2$ photocatalysts for the purification of water have been investigated. The samples were characterized by scanning electron microscopy (SEM), specific surface area (BET), X-ray diffraction analysis (XRD), and energy dispersive X-ray spectroscopy (EDX). The photocatalytic activities were evaluated by the photocatalytic oxidation of methylene blue (MB) solution. It was found that the prepared Fe-AC/Ti$O_2$ composites have an excellent photocatalytic under visible light irradiation. A small amount of Fe ions in the AC/Ti$O_2$ composites could obviously enhance their photocatalytic activity. The high activities of the Fe-AC/Ti$O_2$ composites could be attributed to the results of the synergetic effects of the enhancement of the Fe element, the photocatalytic activity of Ti$O_2$, and the adsorption of AC.

• The Journal of the Acoustical Society of Korea
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• v.15 no.2E
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• pp.63-75
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• 1996

The squeal vibration of a drum is the major source of brake noise. In this system the binary flutter model of squeal vibration was employed for the drum brake of a passenger car. The vibration analysis of a drum brake was performed by using normal modes, which are obtained by variational method. An improved method for the estimation of shoe modes is proposed and the results are compared with the exact solutions. Numerical results for the coupled system of drum and shoes good agreement with the results of experimental model analysis and those obtained by FE analysis.

• Elastomers and Composites
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• v.44 no.3
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• pp.290-298
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• 2009

In this paper, the Fe-activated carbon fiber (ACF)/$TiO_2$ composite catalysts were prepared by a sol-gel method. The synthesized photocatalysts were used for the photo degradation of Methylene blue solution under UV light. From Brunauer-Emmett-Teller measurements (BET) data, it was shown the blocking of the micropores on the surface of ACF by treatment of Fe and Ti compound. As shown in SEM images, the ferric compounds and titanium dioxides were fixed onto the ACF surfaces. The result of X-ray powder diffraction showed that the crystal phase contained a mixing anatase and rutile structure and the 'FeO+$TiO_2$' from the composites. The EDX spectra for the elemental analysis showed the presence of C, O, and Ti with Fe peaks. Degradation activity of MB could be attributed to +OH radicals derived from electron/hole pair's reactions due to photolysis of $TiO_2$ and photo-Fenton effect of Fe.

• Architectural research
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• v.16 no.1
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• pp.27-35
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• 2014

Nonlinear analysis of reinforced concrete structures is carried out by using Reissner-Mindlin (RM) shell finite element (FE). The brittle inelastic characteristic of concrete material is represented by using the elasto-plastic fracture (EPF) material model with the relevant material models such as cracking criteria, shear transfer model and tension stiffening model. In particular, assumed strains are introduced in the formulation of the present shell FE in order to avoid element deficiencies inherited in the standard RM shell FE. The arc-length control method is used to trace the full load-displacement path of reinforced concrete structures. Finally, four benchmark tests are carried out and numerical results are provided as future reference solutions produced by RM shell element with assumed strains.

• Applied Chemistry for Engineering
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• v.26 no.5
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• pp.575-580
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• 2015

Pd/C catalysts were prepared by various preparation methods such as ion exchange, impregnation and polyol method and also characterized by nitrogen adsorption-desorption isothermal, XRD, FE-TEM and CO-chemisorption. The activities of these catalysts were tested in the hydrogenation of cyclohexene to cyclohexane. Catalytic activities of Pd/C catalysts were found to be effected by the chosen preparation methods. Pd dispersions of each Pd/C catalysts prepared by ion exchange, impregnation and polyol method were 17.55, 13.82% and 1.35%, respectively, confirmed by CO-chemisorption analysis. These were also in good agreement with the FE-TEM results. The Pd/C catalyst prepared by ion exchange method exhibits good performance with the cyclohexene conversion rate of 71% for 15 min. These results indicate that Pd/C catalyst having higher dispersion and lower particle size is in favor of hydrogenation cyclohexene and also Pd dispersion increases with the increment of catalytic activity.

• Structural Engineering and Mechanics
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• v.65 no.2
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• pp.173-181
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• 2018

In this paper, finite element (FE) model updating based on multi-objective optimization with the surrogate model for a steel plate girder bridge is investigated. Conventionally, FE model updating for bridge structures uses single-objective optimization with finite element analysis (FEA). In the case of the conventional method, computational burden occurs considerably because a lot of iteration are performed during the updating process. This issue can be addressed by replacing FEA with the surrogate model. The other problem is that the updating result from single-objective optimization depends on the condition of the weighting factors. Previous studies have used the trial-and-error strategy, genetic algorithm, or user's preference to obtain the most preferred model; but it needs considerable computation cost. In this study, the FE model updating method consisting of the surrogate model and multi-objective optimization, which can construct the Pareto-optimal front through a single run without considering the weighting factors, is proposed to overcome the limitations of the single-objective optimization. To verify the proposed method, the results of the proposed method are compared with those of the single-objective optimization. The comparison shows that the updated model from the multi-objective optimization is superior to the result of single-objective optimization in calculation time as well as the relative errors between the updated model and measurement.

• Journal of the Korean Chemical Society
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• v.35 no.6
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• pp.617-624
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• 1991

Nonstoichiometric solid solutions of $Y_{1-x}A_xFeO_{3-y}$ (A = Ca, Sr) systems with perovskite structure were prepared for x = 0.00, 0.25, 0.50, 0.75 and 1.00 at 1200$^{\circ}C$ under atmospheric pressure, respectively. Crystallographic structures of the solid solutions of all compositions have been determined by the analysis of X-ray diffraction patterns. Reduced lattice volume of the $Y_{1-x}Ca_xFeO_{3-y}$ system was decreased with increasing x value and that of the $Y_{1-x}Sr_xFeO_{3-y}$ system was increased with increasing the x value. The mole ratios of $ Fe^{4+}$ to $ Fe^{3+}$, ${\tau}$, values in the solid solutions have been determined by Mohr salt's method of analysis and then the mixed valency was identified by Mossbauer spectroscopic analysis at 298 K. The y values were calculated from the x and ${\tau}$, and then nonstoichiometric chemical formulas were fixed. The conduction mechanism could be explained by hopping model of the conduction electrons between the mixed valence states.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.766-771
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• 2001

The package used to transport radioactive materials, which is called by cask, must be safe under normal and hypothetical accident conditions. These requirements for the cask design must be verified through test or finite element analysis. Since the cost for FE analysis is less than one for test. the verification by FE analysis is mainly used. But due to the complexity of mechanical behaviors. the results depends on how users apply the codes and it can cause severe errors during analysis. In this paper, finite element analysis is carried out for the 9 meters free drop and the puncture condition of the hypothetical accident conditions using LS-DYNA3D and ABAQUS/Explicit. We have investigated the analyzing technique for the free drop impact test of the cask and found several vulnerable cases to errors. The analyzed results were compared with each other. We have suggested a reliable and relatively simple analysis technique for the drop test of spent nuclear fuel casks.

• Journal of Magnetics
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• v.19 no.2
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• pp.126-129
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• 2014

We report the crystallographic and magnetic properties of $Ni_{0.3}Fe_{0.7}Ga_2S_4$ by means of X-ray diffractometer (XRD), a superconducting quantum interference device (SQUID) magnetometer, and a M$\ddot{o}$ssbauer spectroscopy. In particular, $Ni_{0.3}Fe_{0.7}Ga_2S_4$ was studied by M$\ddot{o}$ssbauer analysis for evidence of spin reorientation. The chalcogenide material $Ni_{0.3}Fe_{0.7}Ga_2S_4$ was fabricated by a direct reaction method. XRD analysis confirmed that $Ni_{0.3}Fe_{0.7}Ga_2S_4$ has a 2-dimension (2-D) triangular lattice structure, with space group P-3m1. The M$\ddot{o}$ssbauer spectra of $Ni_{0.3}Fe_{0.7}Ga_2S_4$ at spectra at various temperatures from 4.2 to 300 K showed that the spectrum at 4.2 K has a severely distorted 8-line shape, as spin liquid. Electric quadrupole splitting, $E_Q$ has anomalous two-points of temperature dependence of $E_Q$ curve as freezing temperature, $T_f=11K$, and N$\acute{e}$el temperature, $T_N=26K$. This suggests that there appears to be a slowly-fluctuating "spin gel" state between $T_f$ and $T_N$, caused by non-paramagnetic spin state below $T_N$. This comes from charge re-distribution due to spin-orientation above $T_f$, and $T_N$, due to the changing $E_Q$ at various temperatures. Isomer shift value ($0.7mm/s{\leq}{\delta}{\leq}0.9mm/s$) shows that the charge states are ferrous ($Fe^{2+}$), for all temperature range. The Debye temperature for the octahedral site was found to be ${\Theta}_D=260K$.